There have been known workpiece feeding apparatus for feeding workpieces between a plurality of working blocks. For example, as disclosed in Japanese laid-open patent publication No. 59-69313, a typical known workpiece feeding apparatus has a hanger suspended from a trolley conveyor and having a suspension support disposed in a traveling direction of the hanger, a vertically movable unit that is vertically movable in response to a signal output from the hanger, and a conveyor positioned on an upper portion of the vertically movable unit for passing through the hanger and comprising a plurality of rotatable rollers. A workpiece placed on the hanger can be transferred to the conveyor.
With the above conventional workpiece feeding apparatus, however, the direction in which the hanger moves is limited by the position where the suspension support is mounted. Specifically, the traveling direction of the hanger is one way only, and if the workpiece placed on the hanger has moved past a working block, then it is extremely difficult for the hanger to reach the working block again. When such a situation occurs, the conventional workpiece feeding apparatus suffers a very low efficiency with which to feed workpieces.
According to the above conventional arrangement, furthermore, the workpiece is placed on the hanger, but is not fixed thereto. The workpiece placed on the hanger is transferred to a processing block, for example, where the workpiece is processed in various processing processes. If the workpiece is displaced for some reasons during its transportation, the workpiece may not be processed quickly and accurately. If the workpiece is displaced a large distance, then it may possibly collide with the hanger or fall off the hanger.
The workpiece which is being transported can be prevented from being positionally displaced by a stopper or the like that is mounted on the placement surface of the hanger and shaped complementarily to the workpiece. However, if a plurality of types of workpieces having different shapes are transported or one type of workpieces is transported in various different postures, then there need to have on hand as many stoppers as the number of types of differently shaped workpieces to be transported or as the number of different postures to be taken by one type of workpieces to be transported. As a result, the number of parts used by the workpiece feeding apparatus is increased, and it is necessary to replace the stopper in use each time the workpiece type to be transported is changed or the transporting posture is changed. Accordingly, the efficiency with which the workpiece feeding apparatus operates is lowered.
Japanese laid-open patent publication No. 60-161825 discloses a conventional arrangement having a carriage for traveling along a feed path while gripping a workpiece with a hand, a dedicated elevator for unloading a workpiece from the carriage, and a dedicated elevator for loading a workpiece onto the carriage.
This conventional arrangement can perform parallel feeding operations with the unloading dedicated elevator and the loading dedicated elevator and hence can avoid a reduction in the efficiency with which to feed workpieces. However, the conventional arrangement is likely to suffer a substantial increase in the equipment cost.
With this conventional arrangement, the carriage has the arm for gripping a workpiece, and the workpiece is firmly gripped by the arm and stably supported thereby against positional displacement. However, the arm itself has a complex mechanism and needs electrical control for some actions to be made thereby. Therefore, the arm is relatively complex in structure and highly costly.
Japanese patent No. 2694546 discloses a conventional arrangement comprising tracks arranged in a crisscross pattern, self-propelled transportation vehicles having drive sources and wheels for traveling on the tracks, and switching means disposed at the intersections of the tracks for turning the tracks to change the direction in which the transportation vehicles travel.
Each of the transportation vehicles of this conventional arrangement is of the self-propelled type having its own drive source for moving on tracks toward a desired working block. Since the transportation vehicle itself has its own drive source, it is relatively heavy. If the rate for feeding workpieces is increased for a higher working efficiency to meet a demand for an increased throughput, then the absolute number of transportation vehicles to be used is increased, and the tracks and the switching means for supporting those transportation vehicles are correspondingly rugged and large in size. Consequently, the overall apparatus is highly expensive and needs to occupy an increased installation space.
Furthermore, if a certain transportation vehicle suffers a fault and stops moving in a certain working block, then since the transportation vehicle is of self-propelled type, it has to be repaired on site or removed from the track by some means because the faulty transportation vehicle, if left on the track, would obstruct the operation of other transportation vehicles. When transportation vehicles suffer a failure, therefore, the machining conveyor apparatus tends to undergo a large drop in the operating efficiency.
Moreover, because the self-propelled transportation vehicles are heavy and cannot move at high speeds, the operating efficiency of the machining conveyor apparatus cannot be expected to be largely improved.
Japanese laid-open patent publication No. 8-39374 discloses a conventional arrangement having a pusher mounted on a trolley chain which is movable in one direction, and a trolley having engaging/disengaging mechanisms disposed symmetrically on front and rear sides of the trolley for engaging the pusher only in one direction, the trolley being movable by the drive power of the trolley chain.
The transportation vehicle used in the conventional arrangement is a non-self-propelled transportation vehicle which is movable by the drive power of the trolley chain. Since the trolley chain is flexible, the transportation vehicle tends to stop at different positions rather than a desired accurate position. In addition, the transportation vehicle moves by having engaging/disengaging mechanisms engage grip members mounted at spaced intervals on the trolley chain, and hence cannot move and stop by gripping the trolley chain at any desired position thereon. Consequently, design limitations are posed on working positions in that if the number of trolleys is to be increased to meet a demand for an increased operating efficiency, then the number of grip members on the trolley chain is unable to keep up with the increased number of trolleys, and the operating efficiency cannot be improved as desired.
It is an object of the present invention to provide a workpiece feeding apparatus which is capable of efficiently transferring workpieces to working blocks and is of a simple arrangement.
Another object of the present invention is to provide a workpiece feeding apparatus which allows a non-self-propelled transportation vehicle, if used, to change its transporting direction as desired, is highly reliable in feeding operation, is of a simple arrangement, can be manufactured at a low cost, is prevented from taking up an increased installation space, can feed workpieces efficiently.
Still another object of the present invention is to provide a workpiece feeding apparatus which is highly reliable in positioning workpieces when they are fed, allows a transportation vehicle to grip a wire as a feeding means at any desired positions thereon for increased positioning freedom to increase a production efficiency, and is of a simple arrangement for making products manufactured thereby inexpensive.
Yet another object of the present invention is to provide a workpiece feeding apparatus which allows a transportation vehicle to grip a wire with increased accuracy, and reduces an amount of wear on the wire thereby to increase the durability of the wire.
Yet still another object of the present invention is to provide a workpiece feeding apparatus which allows workpieces to be positioned easily and reliably without the need for dedicated parts when the type of workpieces to be fed is changed or a transporting posture in which to feed workpieces is changed.